What a BIS-mimic project says about the index's smoothing¶

The openeeg project reproduces the BIS index from the raw EEG and infers each case's smoothing setting: about 80% of its cases come out at 15 s. Its alignment cannot serve as a timing reference.

Background¶

The BIS index is the monitor's EEG features smoothed over a window the operator chooses, and VitalDB does not record the setting.

Data¶

No VitalDB data were analysed here: the openeeg repository (commit bd476c5, 2 June 2026), its code and documentation, were read. The figures quoted (about 80% of its cases at the 15 s smoothing setting) are the project's own, from its VitalDB cases.

Method¶

The project's code and documentation were read for how it infers the smoothing and how it aligns index and EEG.

Results¶

• Smoothing setting: inferred per case by smoothing its own unsmoothed prediction with each candidate and keeping the closest match to the recorded index; about 80% of cases come out at 15 s. Modelled as an exponential average, the index then trails the EEG by about (W − 1)/2 s: about 7 s at 15 s and 15 s at 30 s, plus processing.
• Not a timing reference, for three reasons: each 1 s feature row is paired with the index at the same second while the EEG behind it covers 2–4 s later; the EEG is loaded onto a fixed 1/128 s grid that absorbs the BIS stamp corrections; and the trained model's inputs include trailing 5–60 s means of its own score, so its output carries an unknown lag.

Discussion¶

The atlas's own fit (How the BIS index trails its EEG) uses no trained model and finds the 15 s setting in about half the good fits. openeeg says nothing about device clocks, so the BIS clock link is unchanged.

Observations it supports¶

References¶

• VitalDB. openeeg: open-source EEG processing for depth of anaesthesia (BIS-mimic algorithms validated against VitalDB). GitHub. ↗